Reproduction steps:
1. Open attached project "terrain_bug"
2. Make sure that "DummyTerrain" and "LayerTest" are included in the build
3. Build and launch the project
4. Notice that the grass is visible (wgrass screenshot)
5. Now build and launch the project without DummyTerrain included
6. Notice that there is no grass anymore (woutgrass screenshot)

Note:
DummyTerrain scene has only three components - Camera, Light and Terrain. Deactivating all three components has no effect on the grass. However deleting Terrain makes the grass to not appear at all.